1. Field of the Invention
The present invention relates to a 4-cycle engine for a motorcycle having a secondary-air supplier that supplies secondary air to exhaust ducts for purging exhaust gas.
2. Description of the Related Art
Conventional 4-cycle engines for motorcycles disclosed in, for example, Japanese Unexamined Patent Application Publication No. 57-79212, Japanese Unexamined Patent Application Publication No. 2000-87739, and Japanese Unexamined Patent Application Publication No. 2001-50044 each have a control valve and check valves provided near the upper portion of a cylinder-head cover. The control valve controls the intake of secondary air and the check valves prevent the backflow of the secondary air.
Because these valves are disposed near the cylinder-head cover, the layout in the vicinity of the engine is highly limited. To prevent an air cleaner disposed directly above the cylinder-head cover from interfering with the control valve and the check valves, which protrude upward from the cover, the air cleaner requires a recessed region in its structure. This inevitably reduces the volume of the air cleaner.